Standards experts have agreed on two ways to measure the traction of a walking surface.

Static coefficient of friction (SCOF) is the force needed to make a still object—such as a shoe—lose its grip and begin sliding sideways.

Dynamic coefficient of friction (DCOF) is the force needed to make an already moving object lose traction as it touches the surface.

SCOF looks like this: You’re standing still when someone starts pushing on your shoes with a pushbroom. Your shoes have all your weight on them, but eventually, with enough force, the pushbroom will win and your feet will go out from under you.

Depending on the surface, this will happen sooner or later. On a hockey rink, you’ll go down pretty quick. But not so fast in, say, a movie theater at end-of-day.

Meanwhile, DCOF is measured a little differently. Imagine yourself walking, with one shoe swinging forward as it always does when you take a step. At the instant your shoe hits the floor, it will either grind to a halt (the desired outcome) or continue forward, losing traction. At the very moment traction fails, the measure of forward force divided by downward force is the DCOF.

In either measure—SCOF or DCOF—we get a number between 0 and 1. A zero would be closer to the ice rink. Traction level 1 is more like a syrup-sticky cinema floor.

Both measurements have value in testing for traction. In the U.S., SCOF is the most common method. In Europe, DCOF is preferred.